1. Field of the Invention
The invention concerns a firing device for a plurality of electric valves, especially thyristors, with each of whose control paths a firing circuit with a detector for electromagnetic radiation is associated with a transmitter which is controlled by a firing control signal and is equipped with a radiator which energizes the individual detectors.
2. Description of the Prior Art
It is known (German Patent No. 1,538,099) to use, for firing an electric valve, particularly a thyristor, a firing circuit which derives the firing energy from the voltage at the anode-cathode path of the valve in question. In this arrangement, a pulse capacitor is used which is charged up by means of this voltage and is discharged, when required, onto the control path of the valve via a switching element. As the switching element, a light-controlled thyristor, in particular, is used, which can be fired by light irradiation from a light source placed some distance away. In this manner, electric potential differences which exist between the light source as the transmitter of electromagnetic radiation and the electric valve, have no effect on the firing. Such a firing circuit will therefore be used preferably for the firing of electric valves for high voltage, particularly of high-voltage thyristors that are used in a rectifier arrangement.
Another possibility of transmitting a firing control signal from a transmitter for electromagnetic radiation to a firing circuit, which is equipped with a detector for this electromagnetic radiation, is described in Swiss Pat. No. 413,993. High-frequency radiation is used here as the electromagnetic radiation. The firing of one or several valves via a high-frequency transmission path is largely free of interference and is suitable particularly for the firing of thyristors which are used in rectifiers in high-voltage d-c transmission systems.
It is an object of the present invention to let the largest possible share of the electromagnetic radiation emitted by the transmitter arrive at the detector, so that in the presence of a firing command a sufficiently large input signal is applied to the firing circuit.